America's democratic norms, then, were born in a context of exclusion. As long as the political community was restricted largely to whites, Democrats and Republicans had much in common. Neither party was likely to view the other as an existential threat. The process of racial inclusion that began after World War II and culminated in the 1964 Civil Rights Act and 1965 Voting Rights Act would, at long last, fully democratize the United States. But it would also polarize it, posing the greatest challenge to established forms of mutual toleration and forbearance since Reconstruction.